Path: chuka.playstation.co.uk!scea!greg_labrec@interactive.sony.com
From: Manny Najera <mnajera@ix.netcom.com>
Newsgroups: scea.yaroze.programming.2d_graphics
Subject: Re: Algorithm to orbit?
Date: Sun, 03 Aug 1997 14:54:22 -0500
Organization: SCEA Net Yaroze News
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>         Ok, now my sprites are happily displaying and rotating, but
> now I'm trying
> to figure out how to use the built-in functions to make one point
> orbit
> another point.  I need the sprite that represents my turret to orbit
> around
> the center of my tank sprite as the tank rotates.
>         I thought I'd store the current position of the turret in an
> SVECTOR,  use
> ApplyMatrixSV() and RotMatrixZ() to perform the appropriate
> calculations,
> then store the results back into the GsSPRITE structure.  But
> where/how do
> I tell such an algorithm where the center of the tank is?
>         Am I heading in the right direction with this, or is there an
> easier/faster way to go about this?

I don't think you'd need anything as complex as matrix math to do
something like this.

All you need is two sprites of the same size.  One sprite is your tank,
and the other is the turrent.  Rotate the turrent, and draw it under or
over the tank.  You can then draw another sprite above all of them to
make the turrent look like it's built into the tank.  As long as both
the turrent sprite and the tank are the same size, the turrent will
always appear to rotate around the center.

People tell me that I don't explain things too well, so just say the
word and I'll spend 5 minutes making a quick demonstation program...

Manny Najera